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xen-devel
Re: [Xen-devel] [Patch] time resolution fix.
On 17 Mar 2006, at 16:11, Dong, Eddie wrote:
I have a much detail description in the attached slide, hope
this helpful.
Well, freezing the TSC while a guest is descheduled is not very nice at
all, but I can imagine it stops you getting time went backwards
messages if you are also forcibly re-setting the TSC on PIT ticks. :-)
The freezing is I guess why you have the new hook schedule_out(), which
I'm also not madly keen on. Especially since this must surely be a
short-term workaround (you don't intend to TSC freeze as long-term
solution, right?).
BTW, due to SMP support and more time resource support (RTC and
ACPI), we are planning to do some design modification to sync all those
different kind of time. This patch is mainly for bug fix that exist for
long time and block SMP effort.
Clearly some effort needs to be applied here. Moving all time emulation
into Xen itself would be a good start (e.g., strip PIT emulation from
qemu-dm).
And the new support should be HVM generic, since there are no
differences in time handling between VMX and SVM that should require
(much) vendor-specific handling I think. If there are, or extra vendor
support appears in future (e.g., I'd like to see guest TSC rate
control, as I've said a few times before ;-) ), then we can add vendor
hooks in later.
In summary, I'm not sure about this patch. I feel that if I take it I'm
encouraging 'onward and upward' development without spending the time
to make sure fundamental abstractions like time are designed and
implemented soundly.
-- Keir
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